Expose cl-csv escape mode option, fix #80.

Some CSV files are using the CSV escape character internally in their
fields. In that case we enter a parsing bug in cl-csv where backtracking
from parsing the escape string isn't possible (or at least
unimplemented).

To handle the case, change the quote parameter from \" to just \ and let
cl-csv use its escape-quote mechanism to decide if we're escaping only
separators or just any data.

See https://github.com/AccelerationNet/cl-csv/issues/17 where the escape
mode feature was introduced for pgloader issue #80 already.

pgloader.1.md

@@ -890,6 +890,13 @@ The `csv` format command accepts the following clauses and options:
 	    when they are to be found within the data fields themselves.
 	    Defaults to *double-quote*.
 
+      - *csv escape mode*
+
+        Takes either the special value *quote* (the default) or *following*
+        and allows the CSV parser to parse either only escaped field
+        separator or any character (including CSV data) when using the
+        *following* value.
+
       - *fields terminated by*
 
 	    Takes a single character as argument, which must be found inside

src/parsers/command-csv.lisp

@@ -69,6 +69,10 @@
                                    escaped-quote-name
                                    separator))
 
+(defrule escape-mode-quote     "quote"     (:constant :quote))
+(defrule escape-mode-following "following" (:constant :following))
+(defrule escape-mode           (or escape-mode-quote escape-mode-following))
+
 (defrule option-fields-escaped-by (and kw-fields kw-escaped kw-by escaped-quote)
   (:lambda (esc)
     (bind (((_ _ _ sep) esc))
@@ -94,6 +98,11 @@
 (defrule option-trim-unquoted-blanks (and kw-trim kw-unquoted kw-blanks)
   (:constant (cons :trim-blanks t)))
 
+(defrule option-csv-escape-mode (and kw-csv kw-escape kw-mode escape-mode)
+  (:lambda (term)
+    (bind (((_ _ _ escape-mode) term))
+      (cons :escape-mode escape-mode))))
+
 (defrule csv-option (or option-batch-rows
                         option-batch-size
                         option-batch-concurrency
@@ -107,7 +116,8 @@
                         option-fields-escaped-by
                         option-fields-terminated-by
                         option-trim-unquoted-blanks
-                        option-keep-unquoted-blanks))
+                        option-keep-unquoted-blanks
+                        option-csv-escape-mode))
 
 (defrule another-csv-option (and comma csv-option)
   (:lambda (source)

src/parsers/command-keywords.lisp

@@ -71,6 +71,8 @@
   (def-keyword-rule "by")
   (def-keyword-rule "escaped")
   (def-keyword-rule "terminated")
+  (def-keyword-rule "escape")
+  (def-keyword-rule "mode")
   (def-keyword-rule "nullif")
   (def-keyword-rule "blank")
   (def-keyword-rule "trim")

src/sources/csv/csv.lisp

@@ -57,6 +57,9 @@
    (escape      :accessor csv-escape	  ; CSV quote escaping
 	        :initarg :escape	  ;
 	        :initform cl-csv:*quote-escape*)
+   (escape-mode :accessor csv-escape-mode ; CSV quote escaping mode
+	        :initarg :escape-mode     ;
+	        :initform cl-csv::*escape-mode*)
    (trim-blanks :accessor csv-trim-blanks ; CSV blank and NULLs
 		:initarg :trim-blanks	  ;
 		:initform t))
@@ -156,6 +159,7 @@
                                       :separator (csv-separator csv)
                                       :quote (csv-quote csv)
                                       :escape (csv-escape csv)
+                                      :escape-mode (csv-escape-mode csv)
                                       :unquoted-empty-string-is-nil t
                                       :quoted-empty-string-is-nil nil
                                       :trim-outer-whitespace (csv-trim-blanks csv)